Cryocooler with oil lubricated compressor

ABSTRACT

A system including (i) a primary loop including a first oil compressor configured to raise the pressure of a refrigerant flowing through the primary loop, an oil separator configured to separate oil contaminant from the refrigerant, a valve configured to return the separated oil back to the first oil compressor, at least one heat exchanger, and a first expansion element; and (ii) a secondary loop including a primary/secondary heat exchanger, the primary/secondary heat exchanger also forming a part of the primary loop; wherein the refrigerant includes constituents (a) that function as a solvent of the oil contaminant which fail to be separated from the refrigerant and (b) that at least substantially condense in the primary/secondary heat exchanger.

[0001] This application is a 35 USC 119(e) non-provisional of U.S.Provisional Application Ser. No. 60/465,175 filed Apr. 23, 2003. Thedisclosure of the provisional application is incorporated herein byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to cryocoolers and moreparticularly to cryosurgery including cryoablation using a cryocooler.

[0004] 2. Description of the Related Art

[0005] The use of freezing temperatures for the therapeutic destructionof tissue began in England in the mid 1800s. See History of Cryosurgery,Gage, A., Seminars in Surgical Oncology 1998; 14:99-109 and Cryosurgery,Rubinsky, B., Annual Review of Biomedical Engineering 2000, 02:157-87.One application of cyrosurgery is endometrial ablation which is ablationof tissue of the inner layer of the uterine wall. Joule-Thomson(hereinafter “JT”) cryocoolers can be either open or closed loop systemssuitable for use in cryosurgical applications such as endometrialablation. The closed loop systems can be either single or dualcompressor systems.

[0006] U.S. Pat. No. 5,758,505 to Dobak et al. describes a dual loopsystem and is incorporated in its entirety herein by reference. FIG. 1is a schematic illustration of a closed JT based cryocooler having aprimary loop 100 and a secondary loop 200. The system includes first andsecond primary heat exchangers 140 and 160, respectively,primary/secondary heat exchanger 240, primary and secondary compressors130 and 230, respectively, and primary and secondary expansion elements150 and 250.

[0007] The primary loop includes the primary compressor 130 whichcompresses a primary gas mixture to a selected pressure and temperature.The primary compressor does not require oil. The high pressure primarygas mixture flows from an outlet of the primary compressor 130, throughthe first primary heat exchanger 140, which can be a miniature heatexchanger located in the handle of a cryoprobe. Specifically, the highpressure primary gas mixture passes through a high pressure passagewayof the first primary heat exchanger 140, where it is cooled to a lowertemperature.

[0008] The high pressure gas mixture then passes through theprimary/secondary heat exchanger 240, specifically through a highpressure primary passageway of the primary/secondary heat exchanger 240,where it is further cooled to a lower temperature. The high pressureprimary gas mixture then passes through a second primary heat exchanger160, specifically through a high pressure passageway of the secondprimary heat exchanger, where it is still further cooled.

[0009] The gas mixture then flows to the primary JT expansion element150. After isenthalpic expansion in the primary expansion element 150the expanded low pressure gas mixture cools target tissue T.

[0010] Then, the low pressure primary gas mixture passes back through alow pressure passageway in the second primary heat exchanger 160, whereit is warmed and through a low pressure passageway in the first primaryheat exchanger 140, where it is warmed even further. The low pressuregas mixture then returns to an inlet of the primary compressor 130.

[0011] The secondary loop 200 includes a high pressure path and a lowpressure path. The secondary loop compressor 230 compresses thesecondary refrigerant to a pressure which can be relatively higher thanthe pressure found in the primary system, since the secondary systemdoes not enter the cannula of the probe. The high pressure secondaryrefrigerant then flows from an outlet of the secondary compressor 230,through the primary/secondary heat exchanger 240, which can also be aminiature heat exchanger located in the handle of the cryoprobe.Specifically, the high pressure secondary refrigerant passes through asecondary high pressure passageway of the primary/secondary heatexchanger 240, where it is cooled to a lower temperature.

[0012] The high pressure secondary refrigerant then passes through asecondary JT expansion element 250. After isenthalpic expansion in thesecondary expansion element 250, the expanded low pressure secondaryrefrigerant passes back through a low pressure passageway in theprimary/secondary heat exchanger 240. The low pressure secondaryrefrigerant then returns to an inlet of the secondary compressor 230.

[0013] A problem with this prior art dual loop system is that it is verysensitive to blockage of the expansion element 150 by freezing of vaporor liquid contaminants. Oil used in a typical commercial refrigerationcompressor is such a contaminant and has a freezing point ofapproximately minus 80 degrees Celsius. In order to avoid blockage dueto oil contaminant, some prior art systems such as the Dobak systemresort to an oil-less compressor; however, those systems prove to becostly and complex.

[0014] Single compressor (oil) closed loop systems are also known. Thesesystems also suffer from blockage in the expansion element due tofreezing of oil contaminants originating in the oil compressor. Further,in a single loop system, there is an inability to phase in operation ofthe dual cooling loops in order to reduce the chance of contaminantscreating a blockage.

SUMMARY OF THE INVENTION

[0015] In view of the above, it is an object of the present invention toprovide single and dual loop refrigeration systems using inexpensive oilcompressors without the side-effect of blockage at the primary expansionelement.

[0016] The present invention achieves this goal by using a refrigerantwhich is a solvent of the contaminant oil.

[0017] The present invention further achieves this goal using a dualloop cooling system including a primary loop including a first oilcompressor configured to raise the pressure of a gas mixture flowingthrough the primary loop, an oil separator configured to separate oilcontaminant from the gas mixture, a valve configured to return theseparated oil back to the first oil compressor when the valve is in anopen state, at least one heat exchanger, and a first expansion element.The cooling system further includes a secondary loop including aprimary/secondary heat exchanger. The primary/secondary heat exchangeralso forms a part of the primary loop. The gas mixture includesconstituents (i) that function as a solvent of the oil contaminant whichfail to be separated from the refrigerant by the oil separator and (ii)that at least substantially condense in the primary/secondary heatexchanger.

[0018] Alternatively, the present invention achieves this goal using asingle compressor system including an oil compressor configured to raisethe pressure of a gas mixture; an oil separator configured to separateoil contaminant from the gas mixture; a first valve configured to returnthe separated oil back to the oil compressor when the valve is in anopen state; a condenser configured to change the phase of the gasmixture from vapor to a vapor and liquid combination; a phase separatorconfigured to separate the liquid from the vapor; and a probe includinga first heat exchanger and a second heat exchanger. The gas mixtureincludes constituents (i) that function as a solvent of the oilcontaminant which fail to be separated from the gas mixture by the oilseparator and (ii) that at least substantially condense in thepre-cooler.

[0019] The present invention also achieves the goal of reducing blockageat the primary expansion element in a dual loop system by startingoperation of the secondary compressor in order to bring theprimary/secondary heat exchanger to a predetermined operatingtemperature; and starting operation of the primary compressor after theprimary/secondary heat exchanger has reached its predetermined operatingtemperature.

[0020] The present invention also achieves the goal of reducing blockageat the primary expansion element in a single compressor system byclosing a valve in order to bring a primary/secondary heat exchanger toa predetermined operating temperature. Then, after the primary/secondaryheat exchanger has reached its predetermined operating temperature, thevalve is opened in order to allow the refrigerant to reach the primaryexpansion element via the primary/secondary heat exchanger.

[0021] Lastly, the present invention achieves the goal of reducingblockage at the primary heat exchanger by vacuum baking the primarycompressor without any oil therein at a predetermined temperature for apredetermined time period; and assembling the cryosurgical systemincluding the baked primary compressor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] A more complete appreciation of the invention and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

[0023]FIG. 1 illustrates a prior art dual loop system;

[0024]FIG. 2 is a schematic illustration of a dual loop system accordingto the present invention;

[0025]FIG. 3 is a pressure enthalpy diagram for the system of the FIG.1;

[0026]FIG. 4 is a schematic illustration of a single loop systemaccording to the present invention;

[0027]FIG. 5a is a flowchart showing the steps for starting operation ofthe dual loop system according to an embodiment of the invention;

[0028]FIG. 5b is a flowchart showing the steps for starting operation ofthe single compressor system according to an embodiment of theinvention; and

[0029]FIG. 6 is a flowchart showing the steps for reducing thecontaminants of a compressor prior to assembling a cryocooler systemaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Referring now to the drawings, wherein like reference numeralsdesignate identical or corresponding parts throughout the several views.FIG. 2 is a schematic illustration of a closed JT based cryocoolerhaving a primary loop 6 and a secondary loop 8. The system includesprimary heat exchanger 24, primary/secondary heat exchanger 22, primaryand secondary compressors 2 and 4, respectively, and primary andsecondary expansion elements 26 and 28.

[0031] The primary loop includes the primary compressor 2 whichcompresses a primary gas mixture to a selected pressure and temperature.The selected pressure is approximately 365 psia. The primary compressoris an oil lubricated compressor such as Danfoss model TLS4.5FCLX. Oillubricated compressors are known to place oil contaminants in the gasmixture of its high pressure output. The high pressure primary gasmixture flows from an outlet of the primary compressor 2, through an oilseparator 10. The oil separator 10 can be for example an oil separatorfrom Temprite model #320. The oil separator 10 removes most of the oilcontaminants, approximately 99 percent, from the gas mixture and returnsthe oil contaminants to the input of the primary compressor 2 via avalve 12. In a preferred embodiment, the valve 12 is a solenoid valve.The solenoid valve is not a flow restrictor such as a capillary, butrather is a mechanism which has an open and closed state. According toan embodiment of the invention, the solenoid valve is opened duringstartup of the compressor 2 for about 5 seconds and is closedthereafter.

[0032] A second output of the oil separator provides the high pressureprimary gas mixture to the primary/secondary heat exchanger 22 (i.e., apre-cooler heat exchanger) via a high pressure primary passagewayprovided in flexline 18. The high pressure gas mixture is at roomtemperature upon exiting the oil separator 10 and entering the flex line18. The flexline 18 is a flexible conduit enclosing the fluid andelectrical lines between a console 16 and a probe 20. Theprimary/secondary heat exchanger 22 cools the gas mixture to a lowertemperature, approximately minus 40 degrees Celsius. The gas mixture isselected so as to fully or partially condense in the primary/secondaryheat exchanger. At least 20 percent of the gas mixture should condense.Further, the constituents of the gas mixture are selected so that thecondensate is a solvent of the oil used by the compressor 2. In apreferred embodiment, the constituents of the gas mixture include R116(C₂F₆). The high pressure primary gas mixture then passes through aprimary heat exchanger 24 (i.e., a recuperator heat exchanger),specifically through a high pressure passageway of the primary heatexchanger 24, where it is still further cooled to a lower temperature ofapproximately minus 80 degrees Celsius.

[0033] The gas mixture then flows to the primary JT expansion element26. After isenthalpic expansion in the primary expansion element 26, theexpanded low pressure gas mixture cools target tissue 30. Because theoil which reaches the primary expansion element 26 is already in a verydilute solution with condensed refrigerants, the likelihood of theexpansion element 26 becoming blocked is reduced significantly.

[0034] Then, the low pressure primary gas mixture passes back through alow pressure passageway in the primary heat exchanger 24. The lowpressure gas mixture then returns to an inlet of the primary compressor2.

[0035] The secondary loop 8 includes a high pressure path and a lowpressure path. The secondary loop compressor 4 compresses the secondaryrefrigerant to a pressure of approximately 300 psia. According to oneembodiment, the secondary refrigerant is R410a. The high pressuresecondary refrigerant then flows from an outlet of the secondarycompressor 4, through a condenser 14. The condenser 14 changes thesecondary refrigerant from a superheated vapor to a sub-cooled liquid.The high pressure secondary refrigerant then flows from the outlet ofthe condenser through the flexline 18.

[0036] The high pressure secondary refrigerant then passes through asecondary expansion element 28. After isenthalpic expansion in thesecondary expansion element 28, the expanded low pressure secondaryrefrigerant passes back through a low pressure passageway in theprimary/secondary heat exchanger 22. The low pressure secondaryrefrigerant then returns to an inlet of the secondary compressor 4.

[0037] The primary compressor 2, the secondary compressor 4, the oilseparator 10, the solenoid valve 12, and the condenser 14 are all housedin console 16. Whereas, the primary/secondary heat exchanger 22, theprimary heat exchanger 24, the primary JT expansion element 26, and thesecondary JT expansion element 28 are located in the probe 20. In oneembodiment, the console 16 is approximately 72 kilograms and 66×36×69cm³. The probe 20 includes a disposable portion which attaches to thedistal end of the probe 20 and provides a sterile cover for the probe20. Only the tip of the disposable probe causes freezing of tissue. Thedisposable probe is a sterile, single use device suitable forintrauterine placement and tissue ablation. It has heating capabilityfor thaw cycles to allow probe removal. The disposable probe includesthermocouples to monitor the tip and catheter temperatures. Thedisposable probe includes an injection port and lumens which allowsaline solution to be injected into the patient. The entire contents ofthe Aug. 13, 2003 Specification, Her Option Cryoablation Therapy Systemis incorporated herein by reference.

[0038] The gas mixture of the primary loop has a freezing point belowthe lowest temperature of the primary cycle which is approximately minus130 degrees Celsius and therefore does not cause blockage of the primaryexpansion element 26. To make this most effective, it is beneficial tophase the operation of the primary and secondary compressors. That is,according to a method of operation shown in FIG. 5a, the secondarycompressor 4 is started in order to bring the primary/secondary heatexchanger 22 to a predetermined operating temperature of minus 50degrees Celsius in step 100. Then, after the primary/secondary heatexchanger 22 has reached its predetermined operating temperature,operation of the primary compressor 2 is begun in step 110. This reducesthe chance of blockage at the primary compressor 24 due to frozencontaminants in the gas mixture of the primary loop. FIG. 3 illustratesthe pressure enthalpy diagram for such a system.

[0039]FIG. 4 illustrates a single compressor system according to anembodiment of the invention. Similar to the dual loop system of FIG. 2,the single compressor system includes a compressor 2, oil separator 10,and valve 12. The compressor is an oil lubricated compressor such asDanfoss model TLS4.5F. As discussed above, oil lubricated compressorsare known to place oil contaminants in the gas mixture of its highpressure output. The high pressure primary gas mixture flows from anoutlet of the compressor 2, through an oil separator 10. The oilseparator 10 can be for example an oil separator from Temprite model#320. The oil separator 10 removes most of the oil contaminants,approximately 99%, from the gas mixture and returns the oil contaminantsto the input of the compressor 2 via a valve 12. In a preferredembodiment, the valve 12 is a solenoid valve. The solenoid valve is nota flow restrictor such as a capillary, but rather is a mechanism whichhas an open and closed state. According to an embodiment of theinvention, the solenoid valve is opened for about 5 seconds and isclosed thereafter.

[0040] A second output of the oil separator provides the high pressureprimary gas mixture to the condenser 14. The condenser 14 changes thesecondary refrigerant from a superheated vapor to a sub-cooled liquid.The high pressure refrigerant which is a mixture of liquid secondaryrefrigerant and vapor primary refrigerant at this point then flows fromthe outlet of the condenser 14 to a phase separator 32. The phaseseparator 32 has two outputs. A first output provides a high pressuregas to a valve 34. The second output provides the refrigerant in aliquid state to the secondary JT expansion element 28 via flexline 18.

[0041] According to an embodiment of the present invention, the valve 34is a solenoid valve. Similar to the method of operation described above,according to an embodiment of the invention illustrated in FIG. 5b,during initial operation of the system, the valve 34 is closed in step150. The valve 34 is closed in order to bring the primary/secondary heatexchanger 22 to a predetermined operating temperature of minus 50degrees Celsius without simultaneous operation of the primary heatexchanger. Then, after the primary/secondary heat exchanger 22 hasreached its predetermined operating temperature, the valve 34 is openedin order to allow the refrigerant to reach the primary heat exchanger 24via the primary/secondary heat exchanger 22 in step 160. This method ofoperation reduces the chance of blockage at the primary expansionelement 26 due to frozen contaminants.

[0042] After the valve 34 is opened, the primary/secondary heatexchanger 22 cools the high pressure gas mixture to a lower temperatureof approximately minus 40 degrees Celsius. The gas mixture is selectedso as to fully or partially condense in the primary/secondary heatexchanger 22. Further, the constituents of the gas mixture are selectedso that the condensate is a solvent of the oil used by the compressor 2.In a preferred embodiment, the constituents of the gas mixture includeR116 (C₂F₆). The high pressure primary gas mixture then passes through afirst primary heat exchanger 24, specifically through a high pressurepassageway of the primary heat exchanger 24, where it is still furthercooled to a lower temperature.

[0043] The gas mixture then flows to the primary JT expansion element26. After isenthalpic expansion in the primary expansion element 26, theexpanded low pressure gas mixture cools target tissue 30. Because theoil which reaches the primary expansion element 26 is already in a verydilute solution with condensed refrigerants, the likelihood of theexpansion element 26 becoming blocked is reduced significantly.

[0044] Then, the low pressure primary gas mixture passes back through alow pressure passageway in the primary heat exchanger 24. The lowpressure gas mixture then returns to an inlet of the primary compressor2.

[0045] The second output of the phase separator 32 provides therefrigerant in a liquid state to the secondary expansion element 28 viaflexline 18. After isenthalpic expansion in the secondary expansionelement 28, the expanded low pressure secondary refrigerant passes backthrough a low pressure passageway in the primary/secondary heatexchanger 22. The low pressure secondary refrigerant then returns to aninlet of the compressor 2.

[0046] The compressor 2, the oil separator 10, the valve 12, thecondenser 14, the phase separator 32, and the valve 34 are all providedin the console 16. Whereas, the primary/secondary heat exchanger 22, theprimary heat exchanger 24, and the primary and secondary expansionelements 26 and 28 are provided in the probe 20. All of the componentsprovided in the console operate at room temperature or hotter, up toapproximately 80-90 degrees Celsius. Hence, the flexline 18 does notrequire insulation in order to transport the refrigerant to and from theprobe 20.

[0047] In order to further reduce the amount of contaminants in therefrigerant due to the oil of the primary compressor, according to anembodiment of the invention illustrated in FIG. 6, the primarycompressor is vacuum baked without any oil therein at a predeterminedtemperature for a predetermined time period in step 200 prior toassembling the cryosurgical system including the baked primarycompressor in step 250.

[0048] According to an embodiment of the invention, the predeterminedtemperature for baking the compressor is 100 degrees Celsius and thepredetermined time period for baking is approximately one week. Thespecific duration of baking is determined by measuring when thecontaminants reach a predetermined low level.

[0049] Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1. A system comprising: a primary loop including, a first oil lubricatedcompressor configured to raise the pressure of a gas mixture flowingthrough the primary loop, an oil separator configured to separate oilcontaminant from the gas mixture, a valve configured to return theseparated oil back to the first oil compressor when the valve is in anopen state, at least one heat exchanger, and a first expansion element;and a secondary loop including a primary/secondary heat exchanger, theprimary/secondary heat exchanger also forming a part of the primaryloop; wherein the gas mixture includes constituents (i) that function asa solvent of the oil contaminant which fail to be separated from therefrigerant by the oil separator and (ii) that at least substantiallycondense in the primary/secondary heat exchanger.
 2. The system of claim1, wherein the constituents of the gas mixture include R116.
 3. Thesystem of claim 1, wherein the gas mixture has a freezing point belowlowest predetermined temperature of the primary loop.
 4. The system ofclaim 1, further comprising a probe.
 5. The system of claim 1, whereinthe valve is a solenoid valve.
 6. The system of claim 1, furthercomprising means for controlling when the valve is open.
 7. The systemof claim 4, wherein the probe comprises a device designed for singleuse, intrauterine placement, and tissue ablation.
 8. A method comprisingthe steps of: providing a dual loop cooling system including a primarycompressor operating on a primary loop, a secondary compressor operatingon a secondary loop, and a primary/secondary heat exchanger shared byboth the primary and secondary loop; starting operation of the secondarycompressor in order to bring the primary/secondary heat exchanger to apredetermined operating temperature; and starting operation of theprimary compressor after the primary/secondary heat exchanger hasreached its predetermined operating temperature.
 9. The method of claim8, further comprising the step of using refrigerant including R116. 10.A system comprising: an oil lubricated compressor configured to raisethe pressure of a gas mixture; an oil separator configured to separateoil contaminant from the gas mixture; a first valve configured to returnthe separated oil back to the oil compressor when the valve is in anopen state; a condensor configured to change the phase of the gasmixture from vapor to a vapor and liquid combination; a phase separatorconfigured to separate the liquid from the vapor; and a probe includinga first heat exchanger and a second heat exchanger; wherein the gasmixture includes constituents (i) that function as a solvent of the oilcontaminant which fail to be separated from the gas mixture by the oilseparator and (ii) that at least substantially condense in the firstheat exchanger.
 11. The system of claim 10, wherein the constituents ofthe gas mixture include R116.
 12. The system of claim 10, wherein thegas mixture has a freezing point below lowest predetermined temperatureof the pre-cooler.
 13. The system of claim 10, further comprising a lineand a console, wherein the line connects the probe and the console andthe console includes the oil compressor, the oil separator, the valve,the condenser, and the phase separator.
 14. The system of claim 13,wherein the line is not insulated.
 15. The system of claim 10, whereinthe first valve is a solenoid valve.
 16. The system of claim 10, furthercomprising means for controlling when the valve is open.
 17. The systemof claim 10, wherein the phase separator operates at room temperature.18. The system of claim 10, further comprising a second valve situatedbetween the phase separator and the probe, and configured to pass thevapor when in an open state to allow operation of the first heatexchanger without simultaneous operation of the second heat exchanger.19. The system of claim 10, wherein the probe comprises a devicedesigned for single use, intrauterine placement, and tissue ablation.20. Method for manufacturing a cryosurgical system, comprising:providing at least one oil compressor including a primary compressor;vacuum baking the primary compressor without any oil therein at apredetermined temperature for a predetermined time period; andassembling the cryosurgical system including the baked primarycompressor.
 21. The method of claim 20, wherein the predeterminedtemperature is 125 degrees Celsius.
 22. The method of claim 20, whereinthe predetermined time period is approximately one week.
 23. A methodcomprising the steps of: providing a single compressor cooling systemincluding, a first heat exchanger, a second heat exchanger, a condenserconfigured to change the phase of a gas mixture from vapor to a vaporand liquid combination, and a phase separator connected to thecompressor via the condenser, configured to separate the liquid from thevapor, and including a vapor outlet and a liquid outlet, wherein thefirst heat exchanger is connected to both the vapor outlet and theliquid outlet of the phase separator, the second heat exchanger isconnected to the vapor outlet after the first heat exchanger, and acontrol valve is situated between the phase separator and the first heatexchanger on the vapor outlet; closing the control valve and startingoperation of the compressor in order to bring the first heat exchangerto a predetermined operating temperature using the liquid from theliquid outlet; and opening the control valve after the closing step inorder to allow flow of the vapor through the first and second heatexchangers.
 24. The method of claim 23, further comprising the step ofusing gas mixture including R116.
 25. The method of claim 23, whereinthe providing step includes the step of providing an oil separator and areturn valve, the oil separator connected between the compressor and thecondenser, the return valve connected to an outlet of the oil separatorand an inlet of the compressor.